1. Field of the Invention
The present invention relates to a coating rod and a producing method therefor, and in particular relates to a coating rod for coating various kinds of liquid substance (coating liquid) on a material to be coated (hereinafter called as web), and for smoothing the liquid substance after coating. The material to be coated is a thin metal plate, a paper, a film and so forth having a sheet shape or a web shape.
2. Description of the Related Art
With respect to coating apparatuses for applying various sorts of coating liquids to a web of a thin metal plate, a paper, a plastic film and so forth, various kinds of apparatuses are known. For example, there are a roll coater, an air knife coater, a coater using a die, and a rod coater.
Among the coating apparatuses, the rod coater is widely utilized, since this coater is a simple coating apparatus and is capable of applying the various sorts of the coating liquids to various kinds of webs. As to the rod coaters, there are two types, in one of which an excess of the coating liquid applied to the web is removed by a coating rod (sometimes called as bar), and in the other of which application to the web and adjustment of a coating-liquid amount are performed by a single coating rod. In both types of the rod coaters, a surface of the coating rod has a plurality of grooves formed in a circumferential direction. In accordance with a depth, a width and so forth of the grooves, are regulated the coating-liquid amounts to be applied to the web and to be removed.
For example, Japanese Patent Laid-Open Publication No. 2001-901 proposes a coating rod having concave portions and convex portions, which are formed at a rod surface in a circumferential direction and are alternately formed in an axial direction of the rod. An upper surface of each convex portion is formed so as to be a flat surface, and a width of this flat surface is adapted to be 10 μm or more. At the same time, surface maximum roughness of the rod surface is 0.05 μm or more and is 0.8 μm or less, and a coating film of a hard material is formed on the rod surface having the above flat surface and the above surface maximum roughness.
In the meantime, Japanese Patent Laid-Open Publication No. 2001-87697 proposes a coating rod whose straightness is 0.25 mm or less per 1 m of the rod, for the purpose of uniform coating. Further, Japanese Patent Laid-Open Publication No. 9-1032 proposes a coating rod having improved abrasion resistance. Regarding this coating rod, uniform coating is formed in a widthdirection of a web in a state that a ratio of Rz to Rmax (Rz/Rmax) is within a range of 0.5 to 1.0, wherein Rz(μm) is the ten point average roughness of a cross section curve in a longitudinal direction of a rod surface and Rmax is maximum roughness. Moreover, a ratio of l to L (l/L) is within a range of 0.2 to 0.9, wherein 1 is a total length of line segments abutting on a material to be coated and L is a measurement length. Further, a peak number Pc of the cross section curve in the longitudinal direction is one or more per 1 mm.
In the above-mentioned coating rods, a surface reforming treatment layer is formed on the rod surface in order to improve the abrasion resistance. However, the surface of the treatment layer has minute irregularity of which the tip is sharp. Thus, if coating is performed as it is, there arises a problem in that scratches are caused on a coating surface. Meanwhile, concavities and convexities for regulating a coating amount are formed on the rod surface. When the convexities have uneven height, there arises a problem in that the highest portion partially abuts on the web to cause scratches. Although the highest portion of the convexities of the rod surface is abraded while coating is performed, the highest portion causes the scratches in an initial stage of usage so that production efficiency is lowered. In the meantime, when the coating film having hardness and abrasion resistance is used, the sharp tip and the highest portion are hardly abraded so that the scratch is caused for a long time.
When the rod itself has deformation of curvature, roundness defect, torsion and so forth, thickness unevenness (hereinafter called as coating unevenness) is caused due to partial difference of a coating amount applied to the coating surface, even thought it is possible to perform coating. Thus, defective products occur at a certain rate.
Occurrence of the scratch and occurrence of the coating unevenness are unknown until a trial of coating is performed. Since the cost for the trial of coating is taken, countermeasure thereof is desired.